1. Field of the Invention
The present invention relates to a nitride-based semiconductor light-emitting device using a nitride-based semiconductor (InxAlyGa1-x-yN: 0≦x, 0≦y and x+y<1), as well as a manufacturing method thereof.
2. Description of the Background Art
Japanese Patent Laying-Open No 10-270761 discloses a structure of a conventional nitride-based semiconductor light-emitting device, which is shown in FIG. 23. In FIG. 23, the conventional nitride-based semiconductor light-emitting device has a structure in which a p-type ohmic contact layer 101, a p-type GaN layer 102, an active layer 103, an n-type GaN layer 104, and an n-side electrode 105 are successively layered on an Al substrate 100.
The conventional nitride-based semiconductor light-emitting device is fabricated in the following manner. Initially, n-type GaN layer 104, active layer 103, and p-type GaN layer 102 are successively layered on a sapphire substrate (not shown), to form a semiconductor layered portion. Thereafter, p-type ohmic contact layer 101, which is an alloyed layer of Ni and Au and readily forms ohmic contact with p-type GaN layer 102, is provided on the entire upper surface of p-type GaN layer 102. Then, Al substrate 100 is attached as a support base on the upper surface of p-type ohmic contact layer 101, with a conductive adhesive such as an Ag paste. The sapphire substrate is then completely removed by polishing. Finally, n-side electrode 105 fabricated from an alloyed layer of Ti and Au, for example, is patterned and formed on the surface of n-type GaN layer 104 exposed by removing the sapphire substrate.
In the conventional nitride-based semiconductor light-emitting device as described above, light emitted from active layer 103 to Al substrate 100 side is reflected at an interface S between p-type GaN layer 102 and p-type ohmic contact layer 101, and extracted to the outside of the device. On the other hand, because Al substrate 100 serving as the support base is not transparent, light extraction efficiency thereof is significantly affected by reflectivity at interface S between p-type GaN layer 102 and p-type ohmic contact layer 101. P-type ohmic contact layer 101, however, is formed with the alloyed layer of Ni and Au. Accordingly, reflectivity at the interface with p-type GaN layer 102 is low, and most part of the light is absorbed.
In addition, though the sapphire substrate is completely removed by polishing, there is inplane variation of several μm in a film thickness of the polished sapphire, even if a high-precision polishing technique is used. Therefore, n-type GaN layer 104 should be formed with a film thickness not smaller than several μm, that is, with a sufficient margin, so as not to have a portion of n-type GaN layer 104 removed by polishing. For such reasons, yield is poor, and manufacturing cost tends to increase.